readTableIndex {R.utils} | R Documentation |
Reads a single column from file in table format, which can then be used as a index-to-row (look-up) map
for fast access to a subset of rows using readTable
().
## Default S3 method: readTableIndex(..., indexColumn=1, colClass="character", verbose=FALSE)
indexColumn |
An single integer of the index column. |
colClass |
A single character specifying the class of the
index column. |
... |
Arguments passed to readTable () used internally. |
verbose |
A logical or a Verbose object. |
Returns a vector
.
Henrik Bengtsson (http://www.braju.com/R/)
readTable
().
## Not run: # File containing data table to be access many times filename <- "somefile.txt" # Create a look-up index index <- readTableIndex(filename) # Keys of interest keys <- c("foo", "bar", "wah") # Read only those keys and do it fast df <- readTable(filename, rows=match(keys, index)) ## End(Not run)